Prom

Prom \PROM\ , noun;
1. A formal dance, especially one held by a high school or college class at the end of an academic year

80's: Glory days for prom dresses (source)

This is an Americanism that dates to the late 19th century. It's short for promenade, which dates to the 1560's as "leisurely walk" from Middle French promenade. The French word comes from se promener ("go for a walk"), which derives from Late Latin promenare ("to drive animals onward"). It's a combination of pro- + minare ("forth" + "to drive animals with shouts").